Solar and gas/diesel generator:

Re: Solar and gas/diesel generator:

Simon,

You might try and stick with one thread about the RO system in Coluombia... There are links to weather, your site, and other bits and pieces of information that you provided that would help size this system without having to go through multiple threads or asking the same questions over...

Either go back to the "main" thread of yours--or transfer the basic information (power requirements, both instantaneous, and average, seasonal variations, etc.). Without the exact requirements (costs, both upfront and possible donations, and expected finacial reserves/ongoing costs down the road)--it would be difficult to craft an optimum system--when most of us probably don't have a clue to the delivered price of solar panels, fuel, parts, skilled labor, etc.

Regarding the use of a generator/solar panels--Calculating the "true" costs (capital, maintenance, fuel, risks, fixed per year, variable per kWhr, etc.) would be the first place to start.

Generally, with fuel costs, you will want the optimum use of fuel (best efficiency). Basically you have two choices (that I see). First choice would be to size the motor to run the RO 24 hours per day (say RO is a 1kW by 24 hour system, or 24 kW by 1 hour). Size the generator to 50-80% of the load would probably give you the best fuel burn.

If, you need to run the RO 24 hours per day (1kW x 24 hours), but only want to run the generator a few hours per day, then you could size the generator to run at, say, 4 hours per day. That would suggest:

Gen Size = (24 kWhrs per day / 4 hours)*1/0.8 batt eff*1/0.85 charge eff + 1kW RO load * 1/0.75 rated load = 9.8kW generator

Notice that just adding batteries and a charger (if AC charger--a 48 VDC generator may save you some fuel/voltage conversion losses) give you an efficiency hit of Eff=0.8*0.85=68% or 32% loss (these are just SWAGS--use real numbers when you get specs).

If you decide to use batteries, then 80-90% of the battery charge "energy" is during the "bulk" or "absorb" stage where you can run the generator near maximum efficiency (and power). As you go for the last bit of charge (and occasional equalization charging, etc.), the amount of current required is much less. And solar panels are a good use for this (quiet, efficient, lower power requirements). Run the generator in the morning, and around noon (or a bit before) put, roughly enough panels to run the 1 kW RO unit + the amount of power to finish charge the batteries. Again, using a SWAG:

Panel Ratings=[{1kW+ (24kWhr/4hour solar charge)*10% daily batt usage final charge*1}/0.66 solar panel derating]=2.4 kW

Anyway--This is how I would start to address the problem. Throw in the costs of fuel, fuel flow per kWhr generated, costs of generators (AC/DC), efficiencies of AC/DC, availability in Columbia of AC/DC/Diesel/Gas/other fuels, etc.

For costs, also need to divide the Capital costs by lifetime (20-25 years for solar panels, 2,000-10,000 hours 500-1,500 hours for portable gas, 6,000-10,000 hours for 1,800 rpm gasoline, and upwards of 20,000-30,000 hours for diesel (range/guesstimate for total overhaul/replacement).

Simon, I would like to see what you find and how you are looking at costs--it would be interesting to see what real numbers you are getting.

-Bill

By the way, 24kWhrs/day is a good deal of electricity. Just as a guess, you are looking at producing 1,600 gallons of water a day (24kWhr per day/0.015kWhr/gal) and that is 24kWhr/day * 30 days per month = 720 kWhrs per month. Here in California that is $70-$140 per month power bill.

Fuel wise, running a 2kW Honda eu2000i generator (pretty efficient small consumer generator) 24 hours per day at 1kWhr will roughly use 1.1 gallons every 4 hours (up to 1,600 watts continuous):

Gas=(1.1 g / 4 hours) * 24 h/d * 30 d/m = 198 gallons of gasoline per month.

Here, that would be $3.40/gallon * 198 = $673 per month just for fuel (and a ~$900 generator that would need to be replaced every 2,000 hours or about 4x per year, at least).

A small diesel might use about 1/2 the gallons per kWhr as the small Honda gasoline example above.

Any way you cut this--you are talking about good sized capital costs, plus the ongoing operational costs.

Problem would be to either find a small prime mover rated diesel generator (~2kW) and run it 24 hours per day, or run a larger one with batteries, or get a larger RO unit + 10kW or so prime mover genset and run it 4-8 hours per day (or what ever fraction your consumers/officials would allow).

Without knowing more about your load's duty cycle and other requirements (and locally available resources)--I am not sure where to head with this.

How much to run power lines and/or water lines from an appropriate source to the point of use. Does all water need to be "biologically pure" or could you pipe lots of "low-mineral content water" with local treatment (lower pressure RO and/or chemical treatment/filtering/etc.).

You know the region--and I obviously don't--but I have seen 100 year old pipes run 20+ miles from a mountain spring for use in-town (gold/silver mining at the time).

I used 1 gallon per day as a one step up from minimal fresh water per person per day. UN was using ~40 gallons per day of fresh water (really 40 liters per day per person) as a point for having a "civilized" amount of fresh water. Using RO to make 40 gallons per day per person sounds expensive. Piping (including water shed/cistern/storage) 40 gallons per day of non-salt water with local treatment for the 1/2-1 gpd per person use seems to a much better long term investment vs reliance on salt water desalination for folks trying to get one step up from a subsistence existence.

Simon, I am not trying to second guess you--I really am interested in your reasoning based on what is available locally.

-Bill

PS: Fix a few small typos... :roll: and now updated/added a few numbers on generator life and fuel consumption...

And for those interested, here is a 2005 Colombian project that uses locally produced bio-diesel at 1.30 Euro per gallon vs the landed cost of 5.50 Euro per gallon in a more remote village... Bio-Diesel production probably does not apply to the arid region that Simon is working with.

http://www.scizerinm.org/biodiesel.html

Re: Solar and gas/diesel generator:

Simon,

It is OK either way to post a new thread or continue in the old--The systems change and morph as more information is gathered (and I am not a moderator--so you can safely ignore my two cents worth )

Sorry about the ColOmbia (I knew that... yea sure...)--I guess you are not doing the system for Washington DC (District of Columbia--).

Don't worry about not posting for a while. No information, can't really post anything.

Take care,
-Bill

Re: Solar and gas/diesel generator:

Mike,

I believe that Simon needs to desalinate sea water... From what I have read, a sea water RO plant needs on the order of 850 PSI of pressure... That is a head of some 1,800 feet (just round numbers).

-Bill